Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional printing is an additive process in which one or more printheads eject successive layers of material on a substrate in different shapes. The substrate is supported either on a platform that can be moved three dimensionally by operation of actuators operatively connected to the platform, or the printhead or printheads are operatively connected to one or more actuators for controlled movement of the printhead or printheads to produce the layers that form the object. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
The production of a three-dimensional object with these printers can require hours or, with some objects, even days. One issue that arises in the production of three-dimensional objects with a three-dimensional printer is consistent functionality of the inkjets in the printheads that eject the ink drops that form the objects. During printing of an object, one or more inkjets can eject material with a drop volume that is less than the desired amount or even clog completely. These volumetric differences can accumulate during the printing of the multiple layers that form an object so the column of material formed by the inkjet ejecting the smaller drops can be shorter than the surrounding material columns formed by the other inkjets. These surface variations can be significant enough to require the scrapping of the object. Because the print jobs can require many hours or multiple days to produce objects, this scrapping of objects can be expensive and time consuming. A printer capable of detecting and identifying inoperative inkjets during printing of an object would be advantageous.